Mouth ulcers — also known as canker sores — are normally small, painful lesions that develop in your mouth or at the base of your gums. They can make eating, drinking, and talking uncomfortable. Women, adolescents, and people with a family history of mouth ulcers are at higher risk for developing mouth ulcers.

Mouth ulcers aren’t contagious and usually go away within one to two weeks. However, if you get a canker sore that is large or extremely painful or if it lasts for a long time without healing, you should seek the advice of a doctor.

Minor ulcers. These are around 2-8mm in diameter and usually clear up in 10 days to 2 weeks.
Major ulcers. These are bigger and deeper, often with a raised or irregular border. This type of ulcer can take several weeks to heal and may leave a scar in the mouth.
Herpetiform ulcers: This type of ulcer is a cluster of dozens of smaller sores the size of pinheads.

You may have a mouth ulcer if you have:

A painful sore or sores inside your mouth, on the tongue, soft palate (the back portion of the roof of your mouth), or inside your cheeks
Sores in your mouth that are round, white, or grey in colour, with a red edge or border
In severe mouth ulcer attacks, you may also experience:

Fever
Physical sluggishness
Swollen lymph nodes

The exact cause of most mouth ulcers is unknown. Stress or tissue injury is thought to be the cause of simple mouth ulcers. Certain foods, including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes and strawberries), can trigger a mouth ulcer or make the problem worse. Sometimes a sharp tooth surface or dental appliance, such as braces or ill-fitting dentures, might also trigger mouth ulcers.

Some cases of complex mouth ulcers are caused by an underlying health condition, such as an impaired immune system; nutritional problems, such as vitamin B12, zinc, folic acid, or iron deficiency; and gastrointestinal tract disease, such as coeliac disease and Crohn's disease.

When you first quit smoking, you may develop more mouth ulcers than normal, but this is temporary.

Some medications, including common painkillers, beta-blockers and some chest pain medications may cause a reaction that leads to mouth ulcers.

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